1. Field of the Invention
The present invention relates to a wafer sheet expanding apparatus for expanding a wafer sheet retained by a wafer ring and a pellet bonding apparatus using thereof.
2. Description of the Background Art
As a machine sequentially picking up a semiconductor pellet from a wafer sheet having pasted thereon a wafer divided in units of a semiconductor pellet that retained by a wafer ring and bonding the picked up semiconductor pellet onto a substrate such as a lead frame or carrier tape, this is known a pellet bonding machine. The pellet bonding machine, in advance of the pickup operation of the semiconductor pellets, removes the slack of the wafer sheet or forms very small gaps between the semiconductor pellets for picking up the semiconductor pellet excellently from the wafer sheet. At this time, these small gaps are formed by stretching of the wafer sheet retained by the wafer ring by the use of a wafer sheet expanding apparatus. A conventional wafer sheet expanding apparatus is described in, for example, Japanese Patent Application Laid-Open No.9-82783.
This wafer sheet expanding apparatus comprises an expanding mechanism, a rotating mechanism, and an XY table. The expanding mechanism stretches a wafer sheet. The rotating mechanism rotates the expanding mechanism. The XY table moves the expanding mechanism in the X and Y directions. Each of the expanding mechanism, rotating mechanism and XY table has drive means such as a motor or air cylinder. And then, when the wafer ring is supplied to the wafer sheet expanding apparatus, first, the expanding mechanism stretches the wafer sheet. Next, the amount of positional displacement in the rotation direction of the wafer (pellet) on the stretched wafer sheet is detected using a camera. In a case where the positional displacement in the rotation direction of the wafer has been detected by the camera, the rotating mechanism makes its rotation in the direction of correcting this displacement. Also, in a case where dividing the wafer into a plurality of equal areas and picking up the semiconductor pellet for each area, the rotating mechanism rotates the expanding mechanism so that the area from which the pellet is to be picked up this time may be located at the pickup position where the pellet is to be picked up by a suction nozzle such as a pellet transfer member. Thereafter, each semiconductor pellet on the wafer sheet is positioned at the pickup position and is picked up by the suction nozzle and bonded to a lead frame or the like.
Meanwhile, in the above-described expanding apparatus, single purpose drive means is used for each of the expanding mechanism and rotating mechanism. This raises the problem that the expanding apparatus becomes large in size and in weight because of the necessity of ensuring the space for disposing the respective drive means with respect to the apparatus. In addition, the drive means for the expanding mechanism and that for the rotating mechanism are very low in the operation rate compared to the drive means for the XY table. Namely, during the pickup operation (pellet bonding operation) of the semiconductor pellet, the drive means for the XY table operates for each pickup of the semiconductor pellet in order to position the semiconductor pellet sequentially at the pickup position. On the other hand, the drive means for the expanding mechanism operates only at the time of expanding the wafer sheet and at the time of releasing the stretched state of the wafer sheet. Also, the drive means for the rotating mechanism operates only at the time of correcting the rotational displacement of the wafer or at the time of changing the pickup area of the semiconductor pellet. Providing the drive means whose operation rate is low individually is not preferable in terms of construction of the apparatus.